1. Field of the Invention
The invention is directed to stripping compositions and processes useful for the roll-to-roll manufacturing of electrophoretic displays.
2. Description of Related Art
The electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon of charged pigment particles suspended in a dielectric solvent. It was first proposed in 1969. The display usually comprises two electrode plates placed opposing each other. One of the electrode plates is usually transparent. An electrophoretic fluid composed of a colored solvent with charged pigment particles dispersed therein is enclosed between the two electrode plates. When a voltage difference is imposed between the two electrode plates, the pigment particles migrate to one side or the other causing either the color of the pigment particles or the color of the solvent being seen from the viewing side.
An improved EPD technology is disclosed in applications, U.S. Ser. No. 09/518,488 now U.S. Pat. No. 6,930,818, filed on Mar. 3, 2000 (corresponding to WO 01/67170), U.S. Ser. No. 09/784,972, filed on Feb. 15, 2001 (corresponding to WO02/65215) now U.S. Pat. No. 6,933,098 and U.S. Pat. No. 6,672,921, all of which are incorporated herein by reference. The improved EPD comprises closed cells formed from microcups of well-defined shape, size and aspect ratio, filled with charged pigment particles dispersed in a dielectric solvent or solvent mixture and sealed with a polymeric sealing layer. The manufacturing of a microcup-based electrophoretic display may be carried out roll-to-roll as disclosed in the applications identified above and as a result, the display cells sandwiched between the two electrode plates may be produced continuously on a web.
To complete the construction of such a display device, the electrode lines of the electrode substrates (or plates) must be exposed and connected to a driver circuitry. In U.S. Ser. No. 10/422,608, filed on Apr. 23, 2003, the content of which is incorporated herein by reference in its entirety, a process for removing (or stripping off) part of the display panel in order to expose and connect the conductor lines on an electrode substrate to a driver circuitry is disclosed. The process involves (1) preparing a display panel having filled display cells sandwiched between a first and a second electrode substrates; (2) removing part of a first electrode substrate by asymmetrical cutting by, for example, a die, diamond or knife or a laser cutting method followed by, for example, peeling to expose the layers underneath (which may include an adhesive layer, a primer layer, a display cell layer and in the case of a display prepared by the microcup technology, the microcup layer and the sealing layer, all of which may be collectively referred to as the “strippable layers”) without touching or damaging the underlying second electrode substrate; and (3) stripping off the exposed strippable layers by a stripping solvent or solution. After stripping, the conductor lines on the second electrode substrate are exposed and ready for connection to a driver circuitry. The process may be repeated to expose the conductor lines on the first electrode substrate.
In this process, an edge coating or adhesive may be used before the stripping step to avoid undesirable undercut or penetration by the stripping solvent or solution into the active display areas.
In the case of in-plane switching EPDs, electrode lines are on only one of the two substrate layers. Stripping is required on the substrate with electrodes.
In this process, one critical step is to remove the strippable layers. However, since the strippable layers are usually good insulators adhering well onto the electrode by UV or thermal curing, removal of these layers by physical peeling tends to damage the conductor lines, particularly when the electrode is made of a thin film conductor on a substrate and, in most cases, the strippable layers cannot be removed cleanly. As a result, the residual strippable layers remaining on the conductor lines inevitably would result in poor electrical connection. A post CMP (Chemical and Mechanical Polishing), chemical microetching or ion milling process may be used after the physical peeling process to remove the remaining strippable layers without damaging the electrode substrate; however such a process could be prohibitively expensive and environmentally unfriendly for some applications.